Abstract:

Objective In order to optimize the structure and performance of core-spun yarns made by air-jet vortex spinning, the paper reports on the effects of core filament types and delivery speed on yarn properties, so as to better predict yarn properties and guide the product development of core-spun yarns based on air-jet vortex spinning.
Method The core-spun yarns were prepared using viscose staple fiber as the sheath and different polyester filaments, including polyester draw textured yarn (DTY), polyester full draw yarn (FDY), and polybutylene terephthalate filament yarn (PBT), as the core filament. Through studying the yarn performance test and scanning electron microscope (SEM) images, the differences between different types of core-spun yarns and pure viscose yarns made by Murata vortex spinning were compared and analyzed, and the effects of core filament types and delivery speed on the core-spun yarn tenacity and elongation, evenness CV value and hairiness H value were investigated using two-factor ANOVA.
Results Due to the existence of core filaments, the mechanical properties of the air-jet vortex spun core-spun yarns are significantly improved than that of staple yarns (Tab. 3). The ANOVA results showed that the type of core filaments were the main factor affecting the performance of core-spun yarns and had a significant effect on breaking strength, elongation and hairiness H value; In the considered range, the delivery speed only had a significant effect on the yarn hairiness H value, but had no significant effect on the yarn strength, elongation and evenness. The interaction of filament types and delivery speed had a significant effect on the breaking strength of core-spun yarns (Tab. 4-7). At any delivery speed, the core-spun yarns containing DTY filaments had the highest breaking strength. Although the strength of PBT filament was second only to DTY filament (Tab. 1), the breaking strength of PBT core-spun yarn was the lowest among the three core-spun yarns. The reason is that the excessive difference in elongation at break between filaments and staple fibers. And the breaking strength of PBT core-spun yarn increased with the increase of delivery speed (Fig. 2). At lower spinning speeds, the increased twist of the staple fibers leads to a decrease in their stretchable distance along the yarn axis, which further exacerbates the different simultaneity of filament and staple fiber breakage, with multiple breakage peaks appearing on the stretch curve (Fig. 3).The elongation at break of PBT core-spun yarn was the largest, followed by DTY and FDY core-spun yarn (Fig. 4). Core-spun yarns with elastic filaments are more easier to adapt to the change in the core-sheath structure and adjust in time during stretching, resulting in higher elongation at break. The evenness CV value of the PBT core-spun yarns were most affected by the delivery speed, while the FDY core-spun yarns were less affected by the delivery speed. This because elastic filaments are more easily deformed in the spinning process. The low delivery speeds contribute to short fiber twisting and improve the yarn evenness. However, for PBT or DTY core-spun yarns, low delivery speeds also increase the probability of deformation of elastic filaments, and bring the risk of yarn evenness deterioration. In order to obtain a better yarn evenness, PBT or DTY core-spun yarns should processed at 380 m/min (Fig. 5). The three types of core-spun yarns were not very different in terms of hairiness H value, and hairiness H value increased with increasing delivery speed (Fig. 6). Because the twisting and wrapping effect of the airflow on the free end of the fiber is weakened during high-speed spinning, the amount of fluffy hairiness of the yarn increases.
Conclusion The tenacity and elongation of air-jet vortex core-spun yarns are obviously affected by the mechanical properties of the core filament. In order to obtain high strength yarns, DTY filament with good strength can be selected as the core, and PBT filament with good elasticity can be selected to improve the elongation at break. However, due to the large difference in the elongation at break between PBT filament and viscose staple fiber, the yarn breaking strength is low when there is a difference in breakage between the sheath and core fibers. Therefore, the breaking strength of PBT core-spun yarn can be enhanced by increasing the delivery speed to improve the simultaneity of fibers breakage. The effect of delivery speed on yarn evenness is also related to the elasticity of the core filament, the lower the speed, the more intense the filament is affected by the high-speed rotating airflow, and the greater the deformation of the elastic filament, resulting in a more negative impact on the core-spun yarn evenness. But for FDY core-spun yarn, the effect of high-speed rotating airflow on staple fiber wrapping is more prominent, so low speed helps to reduce the yarn's evenness CV value. In addition, the lower delivery speed allows the staple fibers to be fully twisted, constraining the yarn body to become tighter, and also helps to improve yarn hairiness.

Key words: air-jet vortex spinning, core-spun yarn, delivery speed, polyester filament, yarn property